The invention relates to a clamping device, particularly a machine vice, having a body element, a jaw immovably attached thereto, and an oppositely placed movable jaw, displacement of which is assured by a drawbar, which drawbar is furnished with a bearing member on which the movable jaw is supported by means of a compression bar, and the movable bar is configured so that it may be arrested with the compression bar at varying distances from the fixed jaw, and in which a force amplifying arrangement is provided.
A machine vice having a force amplifying arrangement is known in the art. The movable jaw is moved against the work piece to be clamped by rotation of an externally threaded sleeve.
A coaxially arranged spindle then acts on a force amplifying arrangement, which creates the necessary clamping force between the fixed and the movable jaws. The hydraulic force amplifying arrangement is located beneath the fixed jaw in the body element. The free extremity of the compression bar forms the primary plunger, which projects into an interior chamber filled with hydraulic fluid. When the primary plunger is moved to the left, hydraulic fluid is forced out of the interior chamber and into a cylinder, pushing a secondary plunger to the left. The surface area of the secondary plunger is significantly greater than that of the primary plunger, so that the transmitted force is amplified. The force exerted in the leftward direction by the secondary plunger is transferred to the spindle, which creates a high tensile force on the spindle. The primary and secondary plungers are arranged in line and always move in the same direction. The construction of the machine vice is accordingly long, which is disadvantageous.
The object of the present invention is to describe a clamping device that is as compactly configured as possible.
The object is solved with a clamping device according to the definition of the species wherein the force amplifying arrangement includes at least one cylindrical tube and at least two plungers that are movable in concentric cylinders, an outer compression plunger and a clamping plungerxe2x80x94preferably attached to the drawbar by a plunger rodxe2x80x94and wherein two compression chambers are provided, an outer, low-pressure chamber and a high-pressure chamber acting on the clamping plunger from the direction of the drawbar, so that a functional connection is established between the two plungers in such manner that at least one rod having a smaller diameter than the diameters of the plungers and which is connected to the outer compression plunger acts on the high-pressure chamber, which is filled preferably with oil or liquid grease. With the proposed construction, it is possible to produce a very short machine vice.
An advantageous simplification in the manufacture of such devices may be achieved if the plungers have the same diameter. This naturally means that the cylindrical tubes must also have the same diameter. This provision allows a degree of standardisation in production.
According to one advantageous configuration, the plungers are arranged in the same cylinder. The single cylinder thus serves as a guide for both plungers. The number of components included in the device is thus reduced by one.
The overall length of the machine vice may be shortened advantageously if the plungers are movably configured facing one another. During clamping, the compression plunger that is moved by the low-pressure chamber advances towards the clamping plunger, which itself advances towards the compression plunger. The gap between the compression plunger and the clamping plunger is connected with the external atmosphere via a hole, so that a build-up of pressure is advantageously avoided.
The force amplifying arrangement is advantageously disposed below the fixed jaw so that it functions as a tractive force amplifying arrangement. Arranging the force amplifying arrangement in the region of the movable jaw would necessitate a longer machine vice.
According to an advantageous improvement of the invention, the force amplifying arrangement is constructed so as to be detachable from the clamping device in the direction of the fixed jaw. This requires that the diameters of the individual components are constructed in tapered manner from the left exterior side of the machine vice towards the opposing side.
Against the event that very high clamping pressures are required, it is advantageously foreseen that the pressurising medium in the high-pressure chamber is oil or liquid grease. Liquid grease has the advantage that it may be insulated considerably more easily from the other components and the atmosphere.
Since compressors are available in all workshops to produce output air pressure up to 10 bar, in an advantageous arrangement the pressurising medium in the low-pressure chamber may be a gas, preferably air or compressed air.
For purposes of automating the machine vice according to the invention, it may be advantageously constructed so that the pressurising medium in the low-pressure chamber is oil or liquid grease. One option for pressurising may consist in the use of pumps. It would then be possible to control the oil pressure in the low-pressure chamber via the pumping capacity.
In order to achieve the simplest possible construction of the machine vice according to the invention, a hole may be advantageously provided preferably centrally on the clamping plunger adjacent the drawbar, through which a rod connected to the outer, compression plunger and establishing the functional connection projects into the high-pressure chamber. As soon as the low-pressure chamber is pressurised, the compression plunger moves with the attached rod towards the clamping plunger. The rod, whose diameter is considerably smaller than that of the compression plunger, is projected farther into the high-pressure chamber, so that the pressure in the high-pressure chamber rises, and the clamping plunger moves towards the compression plunger. At the same time, the clamping plunger exerts a corresponding tractive force on the drawbar. Tilting and twisting effects are advantageously prevented by the central arrangement of the hole. Moreover, the guidance of the compression plunger is assured at the same time by the guidance of the rod in the central hole.
In a particularly practical configuration, the rod has the form of a hollow rod with an interior pressure adjustment mechanism for adjusting the pressure in the high-pressure chamber. The constant movement of the clamping plunger causes losses due to slippage in the area of the seals. This in turn necessitates subsequent adjustment of the pressure in the high-pressure chamber. This pressure adjustment mechanism advantageously comprises a displacement plunger that may be twisted towards the high-pressure chamber on a screw thread. This increases the pressure of the pressurising medium in the high-pressure chamber.
One essential measure to avoid bouncing effects when the high-pressure chamber is pressurised is advantageously the provision of vent screw to allow air to escape from the high-pressure chamber. Maximum pressures may only be achieved with a high-pressure chamber from which all air has been purged.
To ensure that the vent screw when applied occupies as little room as possible, it is advantageously provided that the vent screw is disposed between a space leading to the atmosphere between the two plungers and the high-pressure chamber. In order to fill the high-pressure chamber, the entire machine vice is rotated from its horizontal operating position into a vertical position. The vent screw is then located at the top end of the high-pressure chamber, thus assuring complete venting.
Since friction occurs when the machine vice is in use, it is advantageously provided that at least one return spring be disposed to return the plungers to a starting position when they are not under pressure. The return spring is advantageously supported with its one spring surface on the tractive plunger and the opposing spring surface on the housing. It is particularly advantageous to arrange multiple return springs in a circle.
One advantageous configuration of the machine vice provides that the force amplifying arrangement includes a cylindrical tube and a clamping plunger that travels inside the cylindrical tube, and that a high-pressure chamber acting on the clamping plunger from the direction of the drawbar is provided and may be pressurised directly with pressurising medium, preferably oil or liquid grease. This configuration is particularly suitable for automating the machine vice. The requisite clamping pressure is supplied by a hydraulic system that introduces the pressuring medium directly into the high-pressure chamber via a delivery connection.
It is advantageously proposed that a device for measuring the pressure in the high-pressure chamber be provided. If the pressure in the high-pressure chamber is determined, the clamping pressure of the machine vice may be calculated and consequently introduction of the pressurising medium may also be automated. The actual pressure may be compared with the reference pressure by appropriate electronic means, so that errors may be detected which, for example, cause the machine tool to be switched off immediately.